An Inertial Navigation System (INS) for a mobile device includes inertial sensors, such as an accelerometer, a gyroscope, and a magnetometer, integrated into the device. The accelerometer and gyroscope measure an acceleration and a rate of rotation of the device, respectively, from which the INS derives or estimates a navigation solution, including position and velocity, based on Newton's Laws. The magnetometer measures the Earth's magnetic field to provide a reference orientation.
Ideally, the INS is a self-contained navigation system that does not depend on an external reference. In practice, however, the INS may rely on low cost inertial sensors configured as Micro Electro-Mechanical Systems (MEMS). MEMS inertial sensors have inherently high rates of measurement error drift and a high level of measurement noise. As a result, errors in the INS navigation solution, such as errors in the estimated position and the velocity, grow relatively quickly over time.
Photogrammetric positioning requires that an observer observe multiple visual features, such as lights, having known positions. The observer may be a camera equipped smartphone, for example. A position of the observer relative to the observed lights can be determined using photogrammetric equations, based on the known positions of the observed lights. Such photogrammetric positioning can provide a relatively accurate position estimate if a sufficient number of visual features can be observed. Frequently, however, movement of the observer and/or line-of-sight blockages between the observer and the lights can interrupt photogrammetric positioning.
Accordingly, especially for a moving observer, photogrammetric positioning tends to provide infrequent yet relatively accurate position estimates with relatively stable errors over time, while INS-derived positioning tends to provide frequent and continuous position and velocity estimates with relatively unstable and diverging errors over time.
In the drawings, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.